With popularization and continuous development of electric vehicles, requirements of people for the electric vehicles are higher and higher. The electric vehicles meet not only sensory and aesthetic demands of people from appearance but also use demands of people from functions and practicability thereof.
There are two existing installation manners for a lithium battery of an electric vehicle, one is front-mounted installation, and the other one is rear-mounted installation. A front-mounted battery box is generally installed on an oblique beam of a vehicle frame, that is, an installation groove provided with a groove wall at periphery is produced in the oblique beam, and the battery box internally filled with a lithium battery is embedded in the installation groove; and in order to enhance stability of the vehicle frame, a cross beam is further arranged on the oblique beam generally, so that the cross beam, the oblique beam and a saddle vertical tube together form a subtriangular shape with stability. However, when taking the battery box out of interior of the installation groove, the battery box needs to be lifted so as to be higher than the groove wall of the installation groove so that to take out the battery box; however, taking-out for the lithium battery is influenced if the cross beam above the oblique beam is designed to be low; moreover, it is more inconvenient due to a high dead weight of the lithium battery; and aesthetic property of the whole vehicle is influenced if the cross beam is designed to be high.